Direction Of Arrival Estimation Algorithm For Wideband Signals

Array signal processing is an important research branch of the signal processing, and has been widely applied in many fields, such as radar, sonar, wireless communications and seismology. With the development of the modern science and technology, wideband signals have been used more and more commonly. To this day, there are many researchers have studied the direction-of-arrival (DOA) estimation for wideband signals, and have made many significant research results. Because broadband signals possess large signal bandwidth and more complex waveform, it is still necessary to further study the DOA estimation for wideband signals. The main objective of this thesis is to study the DOA estimation technology for wideband signals by using uniform linear array, and the mathematic model of wideband array signals and the theory of matrix analysis are the underlying basis. The main contributions of the thesis are listed as follows:Firstly, we propose an extended test of orthogonality of projected subspaces algorithm (ETOPS) based on the incoherent signal subspace method (ISSM). By using more information from several reference frequencies, ETOPS overcomes the problem existed in TOPS that it is difficult to choose the optimal frequency, and its performance outperforms that of TOPS with arbitrarily chosen reference frequency.Secondly, based on the test of orthogonality of frequency subspaces algorithm (TOFS), we propose a new DOA estimation method for wideband uncorrelated and coherent signals by using the spatial differencing technique and the spatial smoothing technique. The method obtains the DOA estimates of wideband uncorrelated signals by using TOFS directly. Then, at each frequency bin, a new matrix is constructed by performing the absolute operation on the eigen-value matrix of the spatial difference matrix. Afterwards, the coherency of coherent signals is removed with the help of the spatial smoothing technique and the DOAs of coherent signals are estimated by applying TOFS accordingly. Because the uncorrelated and coherent signals are resolved separately, the method is suitable to the scenario that the number of array elements is larger than that of signals.Thirdly, the performance of most of the existing wideband DOA estimation methods degrades severely when the array noise is correlated. Based on the matrix transformation technology and focusing technology, two DOA estimation algorithms for wideband coherent signals are proposed in the presence of unknown correlated noise, whose covariance matrix is of Toeplitz structure. By using spatial differencing technique, the effect of correlated noise with Toeplitz-structure covariance matrix is removed. Afterwards, the two methods make use of different ways to estimate the DOAs of wideband coherent signals. In the first algorithm, by taking the absolute value of eigenvalue matrix of the spatial difference matrix at each frequency bin, a new matrix is constructed accordingly. Then, the focusing operation is performed with the exploitation of the focusing rule in rotation signal subspace method. Finally, the DOAs of wideband coherent signals can be estimated by applying MUSIC (multiple signal classification) on the newly coherently averaged covariance matrix. In the second algorithm, by performing the squaring operation on the spatial difference matrix at each frequency bin, a new matrix is construted. Then, the focusing operation is performed accordingly. Finally, the DOAs of wideband coherent signals can be obtained by exploiting the propagator method to the newly coherently averaged covariance matrix. Although the estimation performance of the two algorithms is almost same, the computational burden of the second one is far less than that of the first one. Therefore, the second one is a more effective DOA estimation method for wideband coherent signals in the presence of unknown correlated noise with Toeplitz -structure covariance matrix.Finally, based on the idea of consistent focusing and the focusing rule of two sided transformation (TCT), we propose a wideband DOA estimation method. By constructing the consistent focusing matrix, the method overcomes the disadvantage that the initial DOAs should be pre-estimated in TCT and it is a low-complexity DOA estimation method for wideband signals.